X-ray spectroscope

ABSTRACT

In an X-ray spectrometer, an X-ray source which uses X-rays generated by irradiating a specimen with a primary electron beam, a curved dispersing crystal to diffract the X-rays and a slit device to take out desired components of the X-rays, are diposed on a Rowland&#39;&#39;s circle. The X-ray spectroscope is so designed that the crystal and the slit device may be rotated about the same crystal maintained in the center of rotation in such a manner that the radius of the Rowland&#39;&#39;s circle is varied while Bragg equation and the condition of convergence are satisfied, and that the radius of curvature of the curved crystal may be varied in accordance with the angle of rotation.

United States Patent Hara Oct. 21, 1975 [54] X-RAY SPECTROSCOPE PrimaryExaminerHarold A. Dixon [75] Inventor. Koulchl Hara, Katsuta, Japan y gor Firm craig & Amend [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22]Filed: May 28, 1974 ABSTRACT pp No 473 898 In an X-ray spectrometer, anX-ray source which uses X-rays generated by irradiating a specimen witha primary electron beam, a curved dispersing crystal to dif- [30]Foreign Application Priority Data fract the X-rays and a slit device totake out desired Ma 30, 1973 Japan 48-59787 Components Of the y arediPOSed on a Rowland's circle. The X-ray spectroscope is so designedthat the 52 US. Cl. 250/276; 250/273; 250/399 crystal and the Slitdevice y be rotated about the 51 Int. Cl. G0lt 1/00 s Crystal maintainedin the center of rotation in 5 Field of Search U 5 7 273 27 7 such amanner that the radius of the Rowlands circle 250/280 399 is variedwhile Bragg equation and the condition of convergence are satisfied, andthat the radius of cur- [56] Ref n e Cit d vature of the curved crystalmay be varied in accordance with the angle of rotation.

6 Claims, 7 Drawing Figures US. Patent Oct. 21, 1975 Sheet1of2 3,914,605

U.S., Patent Oct. 21, 1975 Sheet 2 of2 3,914,605

X-RAY SPECTROSCOPE BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to an X-ray spectrometer used in, forexample, the electron probe microanalysis.

2. Description of the Prior Art In general, as electronic apparatuseswhich are used to analyze the constituent elements of a specimen by theuse of X-rays, are known an electron probe microanalyzer and a scanningelectron microscope. The principle of operation of these apparatuses isas follows. Namely, a primary electron beam emitted from an electron gunin vacuum is energized by an anode structure up to a level of l 5O KeV,the high-energy electron beam is then focussed through a plurality ofelectron lenses to have a tiny diameter of 50 5000 A, the very thinelectron beam is bombarded on a specimen, and the elemental analysis inan infinitensimal region of the specimen is performed by detecting witha detector the X-rays emitted from the region.

In order to detect the secondary X-rays produced from the specimen as aresult of impact by the primary electron beam, a detector having anenergy proportionality, e.g. a scintillation counter or a semiconductorX-ray detector recently developed, may be used. Moreover, as the methodfor detecting X-rays are the nondispersion type spectrometry and thedispersion type spectrometry. The former is to detect with suchdetectors as mentioned above the X-rays emitted directly from a specimenand to electrically measure the pulse height value of the detectedoutput while the latter uses such a dispersion element as a diffractiongrating or a single crystal. According to the non-dispersion typespectrometric method, the devices like detectors etc. have only to befixedly placed near the specimen and therefore there is no need for thatmechanism to put the devices in motion which are necessarily provided inthe dispersion type spectrometric method. This may be said to be a greatadvantage. In this method, however, even if a semiconductor X-raydetector is used, the wavelength resolution is lower by a digit than inthe dispersion type spectrometric method and therefore there is adrawback that the discrimination between elements whose atomic numbersare near one another is impossible. On the other hand, the dispersiontype spectrometric method has an excellence of wavelength resolutionover the non-dispersion type method, but it needs a driving mechanism tomove the dispersion element and the X-ray detector along the Rowlandscircle. Accordingly, the mechanical structure of the dispersion typemethod is complicated and the volume of the X-ray spectrometeraccommodating the driving mechanism is large, so that it is hardlypossible from the structural point of view to provide the X-rayspectrometer within a limited space near the specimen chamber of theX-ray analyzer.

SUMMARY OF THE INVENTION One object of the present invention is toprovide an X-ray spectrometer for an X-ray analyzer, having a simplemechanical structure.

Another object of the present invention is to provide an X-rayspectrometer for an X-ray analyzer, which is small in size.

An additional object of the present invention is to provide an X-rayspectrometer for an X-ray analyzer, which is low in cost.

A further object of the present invention is to provide an X-rayspectrometer .for an X-ray analyzer, which can cover the whole range ofwavelengths of X-rays used in the X-ray analysis.

According to the present invention, which has been made to attain theobjects mentioned above, there is provided an X-ray spectrometer whereinan X-ray source which is the surface of a specimen and emits X- rayswhen the primary electron beam bombards the surface, a curveddiffraction crystal to diffract the X- rays and a slit device throughwhich the desired components of the scattered X-rays are taken out, aredisposed on a Rowlands circle, wherein the slit device can be rotatedabout an axis of rotation which passes through the center of the curvedcrystal and wherein the curved diffraction crystal can be replaced byany one of other plural curved diffraction crystals having differentradii of curvature, according to the angle of rotation.

The above and other objects features and advantages of the presentinvention will be apparent when the following description of thisspecification will be read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 schematically illustrates theprinciple of a dispersion type X-ray spectrometric method.

FIG. 2 schematically illustrates the principle of an X-ray spectrometricmethod with straight-forward system for curved crystal as one of thedispersion type X-ray spectrometric methods.

FIG. 3 schematically illustrates the principle of an X-ray spectrometricmethod with rotating system for curved crystal as one of the dispersiontype X-ray spectrometric method.

FIG. 4 schematically illustrates the principle of an X-ray spectrometeraccording to the present invention.

FIG. 5 shows a one embodiment of an X-ray spectrometer according to thepresent invention.

FIG. 6 is a longitudinal cross section of a spectrometer as shown inFIG. 4.

FIG. 7 is a modification of the spectrometer shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the description of anembodiment of the present invention, the principle of the dispersiontype X-ray spectrometric method will be explained with the aid of FIGS.1, 2 and 3.

FIG. 1 diagrammatically illustrates the principle of a dispersion typeX-ray spectrometric method using an electron probe microanalyzer (EPMA)or a scanning electron microscope (SEM).

An electron gun I emits primary electron beam 2, which is energized byan anode 3 up to an energy level of l 50 KeV. The energized electronbeam 2 is then focussed by electronic lenes 4, 5 and 6 to have a verysmall diameter of 50 5000 A and the very thin electron beam serving asprobe bombards a specimen 7. Thereby, secondary X-ray are emitted fromthe specimen 7 over a solid angle of 211' steradians. Namely, the pointto be analyzed on the surface of the specimen 7 forms an X-ray source 8and some parts of all the generated X-rays 9 having a great number ofwavelengths are diffracted by a dispersion element, i.e. a diffractioncrystal 10.

The diffracted X-rays are the characteristic X-rays which havewavelength proper to each of elements constituting the specimem 7 andthe characteristic X-rays are detected, after having been passedthroughan exit slit ll-for X-rays, by a detector 12 to be converted tothe corresponding electric signals.

In the X-ray diffraction, the Bragg equation such that nk 2d sin 6, mustbe satisfied, where n is the order of diffraction, the wavelength ofincident X-ray radiation, a the interplanar spacing of lattice planes ofthe diffracting crystal, and the angle of diffraction. In orderto obtaina high L-B'ratio (Line to Background Ratio), a curved crystal must beused as diffraction element and moreover the condition of convergencesuch that I= 2r sin 0 must also be satisfied. In this case, it isneedless to say that the X-ray source 8, the center C of the diffractioncrystal l0 and the center D of the exit slit are all situated on aRowlands circle having a radius r. In the above-mentioned equation, I isthe distance from the X-ray source 8 to the center of the diffractioncrystal l0 and from the center of the crystal 10 to the center of theexit slit 11, r is the radius of Rowlands circle and 0 is the angle ofdiffraction. Usually, as such a curved diffraction element is used aJohann type curved crystal in which radius of curvature of thediffracting surface is 2r, or a Johansson type curved crystal which isproduced by bending a crystal so that it may have a radius of curvatureof 2r and then by cutting the crystal in such a manner that the radiusof curvature of the crystal surface is reduced to r.

In general, the range of wavelengths of X-rays used in the X-rayanalysis is 0.7 to 120 A. In order to diffract X-rays having such a widerange of wavelengths, a large number of diffraction crystals need to beused in a change-over manner so that a range of wavelengths may beallotted to each crystals. For example, to a diffraction crystal of LiF(Lithium fluoride) is allotted a range of wavelengths 0.7 3.5 A, and, inlike manner, wavelengths 2.4 9.7 A to ADP (Ammonium dihydrogenphosphate), 5.8 24 A to RAP (Rubidium acid phthalate), 22 92 A to STE(Stearate), and 29 120 A to LIG (Lignocerate), these allotments beingrough.

FIG. 2 shows only principal portions in FIG. 1, in which is illustratedhow the range of the wavelengths allotted to each crystal is covered.Throughout the figures, the same reference numerals and characters areapplied like parts and items as in FIG. 1. Now, suppose that the center0 of the Rowlands circle 13 is rotated through an arbitrary angle aboutthe X-ray source 8 defined as the center of rotation and that a newRolands circle formed as a result of the rotation is indicated at 13with a center 0. The straight line is drawn from the position S of theX-ray source 8 to the center C of the crystal l0 and let theintersection of the Rowlands circle 13' and the extension of thestraight line be indicated by C. The centerC of the crystal 10 is movedto the point C andthe crystal 10 after displacement is labeled with anew reference numeral 10. The distance between the points S and C isalso assumed to be 1'. Further, another point D is selected on theRowlands circle 13 in such a manner that the distance from the point Cto the point D is l. The center D of the slit ll moved to the point Dand the slit 11 after displacement is labeled with a new referencenumeral 1 l In this way, the points C and D on the Rowlands circle 13are transferred through the rotation respectively to the points'C and Don the Rowlands circle 13' while the point S remains stationary. In thiscase, also, the above mentioned Bragg equation and condition ofconvergence are both satisfied. As apparent from the Bragg equation, thewavelengths of the characteristic X-rays obtained from the Braggequation depend upon the angles of incidence of the X-rays falling uponthe diffraction crystal, or diffraction angle 6, so that the wavelengthA of the characteristic X-rays obtained before the rotation of theRowlands circle is such that nh 2d sin 9 while the wavelength A of thecharacteristic X-rays obtained after the rotation is such that n 2d sin0.

This means that if the angle 6 of diffraction of a single diffractioncrystal is changed, under the above mentioned conditions, by rotatingthe Rowlands circle,

then the X-rays within the range of wavelengths allotted to the crystalcan be continuously diffracted. This way of operation is calledwavelength scanning and used as one of analyzing methods of detectingthe existence of certain elements in a specimen.

The foregoing lines have been given to the description of the principleof the X-ray analysis based on the X-ray spectrometric method withstraightforward system for curved crystal. As a similar spectrometricmethod is known the X-ray spectrometric method with rotating system forcurved crystal. The principle of the method will be described withreference to FIG. 3. The Rowlands circle 13 having a radius r passesthrough the point S of the X-ray source 8 on the specimen 7 and is fixedstationary. In order to satisfy Bragg equation, the center C of thediffraction crystal 10 and the center D of the exit slit 11 near theX-ray detector 12 are located on the Rowlands circle 13 in such a mannerthat SC CD I. In this case, the diffraction angle of the crystal is 6.If it is required to change the diffraction wavelength A, the points Cand D have only to be transferred, as shown in FIG. 3, to new points Cand D on the fixed Rowlands circle 13 in such a manner that SC CDl'.Namely-, since, even after the displacement, the respective pointssatisfy the Bragg equation and simultaneously the diffraction anglechanges from 0 to 0,then the wavelength A of the characteristic X-raysobtained as a result of this displacement is such that A 2d sin 0'.

In the two dispersion type spectrometric methods described above, thewavelength A is changed by changing the distance 1 between the points Sand C or C and D, that is, by moving the Rowlands circle itself or thediffraction crystal and the exit slit along the Rowlands circle in sucha manner that the Bragg equation and the condition of convergence areboth satisfied. This can be recognized also from the expression A=I'(d/r) (here n l) which can be obtained from n )t 2d sin 0 and l 2rsin 0.

Of the two dispersion type spectrometric methods described above, themethod with rotating system for curved crystal has a drawback that asthe angle 0 of dif-- intensity of the produced X-rays are sometimes toolowfor actual analysis. On the other hand, according to the method withstraightforward system for curved crystal, as shown in FIG. 2, the angleof the X-rays leaving the specimen is kept constant and therefore thismethod may be claimed to be an effective spectrometric method whicheliminates such a drawback as inherent to the previous method.

In these methods, however, the radius of the Rowlands circle is keptstationary and there is a merit that a diffraction crystal having thesame radius of curvature can be used while there is needed a drivingmechanism to move the diffraction crystal and the exit slit in such amanner that the Bragg equation and the condition of convergence are bothsatisfied since the crystal and the slit (inclusive of the X-raydetector) are moved on the Rowlands circle or the Rowlands circle itselfis rotated. Accordingly, the driving mechanism needs to have a widerange of movement and a high accuracy so that the structure iscomplicated, large and costly. Moreover, it is very difficult from thetechnical standpoint to install a large spectrometer including such adriving mechanism within a limited space in the vicinity of the smallspecimen chamber of an X-ray analyzer. The reproducibility of the X-rayanalyzer is largely affected by the mechanical precision of the drivingmechanism and nowadays users require a reproducibility such as producinga wavelength difference less than 5/ 10,000 A between detectedwavelengths of a characteristic X-ray so that it is of technicaldifficulty to attain a reproducibility corresponding to a wavelengthdifference less than 5/ 10,000 A with the spectrometer having such acomplicated mechanism as described above. It is needless to say thatsince the inside of the spectrometer is kept in high vacuum it is veryessential to reduce the size of the spectrometer.

FIG. 4 is a diagram useful to explain the principle of an X-rayspectrometer according to the present invention. The basic conception ofthe conventional X-ray spectrometric methods described with FIGS. 2 and3 is that the characteristic X-rays having different wavelengths arediffracted by changing l in the formula A I X d/r obtained from theBragg equation and the condition of convergence and by maintaining theradius r of the Rowlands circle constant. On the other hand, thefundamental feature of the present invention is that the characteristicXrays having desired wavelengths are obtained by changing the radius ofthe Rowlands circle and maintaining the quantity 1 constant. Referenceshould now be had to FIG. 4. A primary electron beam 2 bombards aspecimen 7 to emit X-rays from the portion serving as an X-ray source 8(represented by a point S). Some part 9 of the X-rays emitted from thesource S is diffracted by a diffraction crystal 10 (its center point isrepresented by C) placed at a distance I from the source S, the angle ofdiffraction being 6. The diffracted characteristic X-rays are passedthrough the center D of an exit slit 1 I placed at a distance [from thecenter C of the diffraction crystal l0 and detected by a detector 12.Here, the points S, C and D are all situated on the Rowlands circle 13having a radius r. Therefore, the wavelength A of the thus diffracted X-rays is such that n A 2d sin 0. Next, the slit 1 l and the detector 12are rotated through an arbitrary angle about the point C of thediffraction crystal as the center of rotation and the slit 1 l and thedetector 12 after the rotation are labeled with new reference numerals11' indicated by the point D. Further, the diffraction crystal 10 is sorotated about its center point C that the X- rays diffracted may beexactly directed to the slit l1 and the detector 12 and the crystal 10after rotation is also labeled with a new reference numeral 10 with anew angle 0 of diffraction. It follows, therefore, thast before therotation of the slit 11 the points S, C and D are situated on theRowlands circle having the center 0 and the radius r in such a mannerthat SC CD I while after the rotation the points S, C and D lie on theRowlands circle having the center 0 and the radius r in such a mannerthat SC CD =1. This means that the characteristic X-rays having a rangeof wavelengths covered by a single diffraction crystal can be obtainedalso in the case where the radius r of the Rowlands circle is changedwhile d and I are kept constant, as is seen from the expression A =1(d/r) (n 1). In other words, in order to obtain characteristic X-rayshaving different wavelengths, the slit 11 is rotated about the point Cof the diffraction crystal 10 while the crystal is so rotated about itscenter C to exhibit desired angles of diffraction.

On the other hand, in order to detect the X-rays obtained through therotation of the slit 1] at as high a sensitivity as possible, thediffracting surface of the crystal must be bent, as described before.The degree of the bend of the diffraction crystal is given by thecondition of convergence: I= 2r sin 0. Therefore, as described with FIG.4, the radius of Rowlands circle is determined by rotating the slit 11so that the radius of curvature of the diffraction crystal is uniquelygiven. Accordingly, for example, in the case where the X-ray analysis isperformed to reveal the elements constituting a part of a specimen, aspecific diffraction crystal must be chosen to obtain the characteristicX-rays having the wavelengths proper to the elements, that is, thediffraction crystal is so chosen as to cover the wavelengths proper tothe elements, and the slit is so moved as to detect the X-rays havingthe required wavelengths, so that the radius of the Rowland 5 circledetermined depending upon the position of the slit will give a suitableradius of curvature of the crystal.

The above described facts will now be explained through concreteexamples. The explanation will be concentrated on the analysis ofextra-light elements such as beryllium (Be), boron (B), carbon (C),nitrogen (N) and oxygen (0). The diffraction crystal used in thisanalysis is a laminated crystal such as stearite having an interplanarspacing d of 50 A. for lattice plane or lignocerate having aninterplanar spacing d of A. Each of the elements has its properdiffracting wavelength A. Namely, oxygen 0 has a characteristicwavelength A of 23.62 A, nitrogen N of 31.6 A, carbon C of 44.7 A, boronB of 67 A, and beryllium Be of I44 A. Accordingly, the radius R ofcurvature of the diffracting crystal for each of the elements can beobtained from the formula I'(d/r) Now, suppose that, in FIG. 4, SC CD =1mm. Then, it follows that l. in the case of detecting oxygen 0, theradius r,, of

curvature of a Rowlands circle 120 X (SO/23.62) 254 mm, hence R 2r 508mm,

2. in the case of detecting nitrogen N, r 120 X (SO/31.6)= mm,

.'.RN= 2r-= 380 mm, 3. in the case of detecting carbon C, r 120 X(SO/44.7) 134.2 mm,

.'.R 2r 268.4 mm,

4. in the case of detecting boron B, r,, 120 X (50/67) 89.5 mm,

R 2r,; 179.0 mm, and 5. in the case of detecting beryllium Be,

r,,,. 120 X (65/114) 68.4 mm R Zr 136.9 mm

Thus, the radius of curvature of each crystal may be determined. TheX-ray analysis of a specimen can be easily performed according to theprocess as follows. A plurality of diffraction crystals whose radii ofcurvature were determined according to such a manner as described above,are mounted previously on a base shown in FIGS. 5, 6 and 7. The slit ismoved to obtain the wavelength proper to the element to be analyzed andthe angle of diffraction is so determined as to direct the X-rays havingthe characteristic wavelengths toward the slit. At the same time, one ofthe diffraction crystals mounted on the base is selected correspondingto the characteristic wavelength and the selected crystal is fixedlyplaced at the point C in FIG. 4.

As described above, if a mechanism is employed in which the center ofthe diffraction crystals is fixed with the slit and the detector rotatedabout the center and in which the crystals are selectively changed overdepending upon the wavelength proper to the element to be analyzed, thenthis mechanism is by far simpler than that usedin thespectrometer withstraightforward system for curved crystal, or the spectrometer withrotating system for curved crystal described with FIGS. 2 and 3. Thesimplification of the mechanism leads to the reduction in size of thespectrometer itself and moreover to the improvements in the mechanicalprecision and the speed of evacuating the spectrometer.

Now, concrete embodiments of the present invention will be described. 1

FIG. 5 shows the principal part of an X-ray spectrometer as oneembodiment of the present invention. When the specimen 7 is bombarded bythe primary electron beam 2, as seen in FIG. 5, the portion 8 of thespecimen 7 emits X-rays. Some part 9 of the X-rays falls upon thediffraction crystal 10 at an angle 0 and then the characteristic X-raysdiffracted by the crystal 10 impinge through the slit 11 onto thedetector 12. In this embodiment, four diffraction crystals 10, 10', 10"and 10" are usedand. they are fixedly mounted on a base 15. The base isrotated by a click-stop mechanism described later. The click-stopmechanism is so designed that the centers C, c" and C' of the crystalsmay be successively brought into the position coincident with the centerC of the crystal 10 shown in FIG. 5 as the base 15 is rotated. The fourplanar surfaces of the base 15 on which the four crystals are attachedare previouslyinclined so that when a desired crystal is set in itsoperating position by rotating the base 15, the angle of diffraction maybe equal to one determined by the desired crystal.

The slit 11 and the detector 12 are fixedly mounted on an arm 14 whichcan be rotated about the point C. If the specimen 7 and the slit 11 areso arranged that the analyzed point S of the X-ray source 8 in thespecimen 7 and the center D of the slit 1 1 may satisfy a condition: SCCD, and. if the center of the slit 11, when the arm 14 is rotated asindicated at 14', 14" and 14" in FIG. 5, is represented successively bythe points D, D" and D, then the conditions are attained such that sc C0CD CD CD, this arrangement being a preferable embodiment of the methoddescribed with FIG. 4.

FIG. 6 is a cross section of the structure shown in FIG. 5. One end ofthe rotary shaft 16 of the base 15 is rotatably supported in the recessin the inner wall 17 of the casing of the spectrometer while the otherend is joumaled in the aperture in the casing wall 17 by means of anO-shaped vacuum seal 18 and capped with a manipulating knob 19 outsidethe casing. By rotating the knob 19 is rotated the base 15. On the innerside of the casing wall 17 is fixed a hollow cylinder 21 having a spring20 therein, recesses are cut at the predetermined positions in the base15 opposite to the cylinder 21, and a protuberance provided at the topof the cylinder 21 is urged by means of the spring 20 into the recess.This arrangement forms the click-stop mechanism. The locations of therecesses are so chosen that the base 15 in rotation may be stopped withthe center of each crystal maintained at the predetermined position. Thearm 14 has a rotary shaft 22'supported in the recess in the casing wall17 and the center axis of rotation of the shaft 22 is in alignment withthe center C of the crystal 10 on the base 15. The rotary shaft 22 ofthe arm 14 on which the slit 11 and the detector 12 are mounted, alsohas worm wheel 24 fixed to the shaft which is engaged with a worm gear23 driven by an external driving mechanism (not shown) placed outsidethe hermetical casing of the spectrometer. The arm 14 is rotated by thedriving mechanism and accordingly the slit 1 l and the detector 12attached thereto are also rotated, so that the characteristic X-raysdiffracted by the crystal 10 can be detected. The rotation of the base15 and the arm 14 is so performed as to satisfy all the conditionsdescribed with FIG. 4. Especially, l is kept constant so that the linearmovement of the diffraction crystals, which is essential in theconventional spectrometer, can be avoided. Moreover, since the center ofrotation of the arm carrying the detector thereon is fixed at astationary point, the structure of the movable part of the spectrometeris much simplified and therefore advantageously conducive to thereduction of the size of the spectrometer. For example, the volume ofthe conventional X-ray spectrometer is 141 while the X-ray spectrometerhaving a mechanism according to the present invention has a volume ofabout 4 I. This means that the ratio of size reduction is less thanonethird. Further, if the size is reduced, the evacuation of the vacuumchamber of the spectrometer is facilitated and the structure of themechanism to determine the positions of the points S, C and D shown inFIG. 4 is simplified. Accordingly, the mechanical error is reduced andparticularly the reproducibility attained by the spectrometer accordingto the present invention corresponds to a wavelength difference equal toor less than 5/l0,000 A.

InFIGS. 5 and 6 is shown an embodiment in which the base 15 and the arm14 are independently rotated but it is also possible to rotate them inan interlocked relation to each other. An interlocking mechanism torotate them together will be described with the aid of FIG. 7. I

In FIG. 7, the rotary shaft 16 of the base 15 is supported at its endsin the recesses in the casing walls 17 and 17' and a cogged wheel 25 isfixedly attached to the shaft 16 near its one end. On the other hand,the rotary shaft 22 of the arm 14 has a cogged wheel 26 attached fixedlythereto, the cogged wheel being coaxial with the worm wheel 24 andengaged with the cogged wheel 25. Therefore, the shaft 16 of the base isrotated as the shaft 22 is rotated. The worm gear 23 is rotated by theexternal driving mechanism so that the arm 14 is rotated, and if thenumbers of the teeth of the wheels 25 and 26 are kept in a predeterminedratio, the base 15 and the arm 14 will be rotated with the angles ofrotation of the base 15 and the arm 14 maintained in a desiredrelationship.

In the embodiment shown in FIG. 5, four diffraction crystals are usedand attached onto the rotary base. However, the number of the usedcrystals is not limited to four. For example, if a spectrometer in whichfive diffraction crystals are mounted on the base is constructed, theentire range of wavelengths, i.e. a range of 0.7 120 A, necessary forthe X-ray analysis of ele ments can be covered by the spectrometeralone. In view of the fact that only two or three diffraction crystalscan be used in a conventional spectrometer and that at least twoconventional spectrometers must be used to cover the entire range of theX-ray wavelengths, the spectrometer according to the present inventionmay be said to eliminate a problem of economy due to the use of pluralspectrometers and a problem of wasted time required in the operation ofchanging over the spectrometers and the diffraction crystals and in theassociated evacuation of the vacuum chamber of each spectroscope.

Further, in the embodiment shown in FIG. 7, the arm 14 and the base 15interlocked to the arm 14 are rotated by an external driving mechanism(not shown), e.g. a manipulating knob in its simplest form, coupled tothe worm gear 23. However, a modfication can be easily thought of bythose skilled in the art, in which, for example, the external mechanismand the worm gear modification as shown in FIG. 7 are not used but inwhich one end of the rotary shaft of the base penetrates the casing wallto serve as a driving end so that the arm is rotated by rotating thedriving end.

As described above, according to the present invention, there can beprovided a spectrometer in which the structure of its movable parts issimplified and reduced in size and which enjoys the functions of aconventional spectrometer to its full extent. Therefore, the presentinvention will be considered to have a great practical merit in thefield of the art.

I claim:

1 An X-ray spectrometer comprising,

an X-ray source;

a plurality of curved crystals for diffracting an X-ray beam emittedfrom said X-ray source, said curved crystals having radius of curvaturedifferent from each other, one of said curved crystals being disposed ata diffracting position where said X-ray beam is diffracted;

a slit means for taking out said diffracted X-ray beam;

a vacuum chamber for arranging therein said X-ray source, said curvedcrystals and said slit means which are situated on a Rowlands circle;

a first rotating means for rotating said slit means by means of a firstrotary shaft, said first rotary shaft having an axis of rotation passingthrough the center of the curved surface of said curved crystal disposedat said diffracting position, and

a second rotating means including a second rotary shaft for rotating oneof said curved crystals onto said diffracting position in accordancewith the rotation of said slit means.

2. An X-ray spectrometer as claimed in claim 1, wherein said firstrotary shaft is coupled with a second rotary shaft penetrating a wall ofsaid vacuum chamber, and a portion of said first rotary shaft protrudingfrom said vacuum chamber is provided with a rotation driving means.

3. An X-ray spectrometer as claimed in claim 1, wherein said secondrotating means includes said second rotary shaft and a rotor fixedthereto, said rotor having on the surface thereof said curved crystalsarranged in such a manner that said curved crystals are disposed on thesame circle having as the center thereof said second rotary shaft.

4. An X-ray spectrometer as claimed in claim 1, wherein said secondrotary shaft penetrates a wall of said vacuum chamber, and a portion ofsaid second rotary shaft protruding from said vacuum chamber is providedwith a second rotation driving means for rotating said rotor.

5. An X-ray spectrometer as claimed in claim 1, wherein said firstrotating means is rotated by a first rotation driving means, and saidspectrometer further comprises an interlocking means for rotating saidsecond rotary shaft in accordance with the rotation of said firstrotating means.

6. An X-ray spectrometer as claimed in claim 1, wherein said secondrotating means is rotated by a second rotation driving means, and saidspectrometer further comprises an interlocking means for rotating saidfirst rotary shaft in accordance with the rotation of said secondrotating means.

1. An X-ray spectrometer comprising, an X-ray source; a plurality ofcurved crystals for diffracting an X-ray beam emitted from said X-raysource, said curved crystals having radius of curvature different fromeach other, one of said curved crystals being disposed at a diffractingposition where said X-ray beam is diffracted; a slit means for takingout said diffracted X-ray beam; a vacuum chamber for arranging thereinsaid X-ray source, said curved crystals and said slit means which aresituated on a Rowland''s circle; a first rotating means for rotatingsaid slit means by means of a first rotary shaft, said first rotaryshaft having an axis of rotation passing through the center of thecurved surface of said curved crystal disposed at said diffractingposition, and a second rotating means including a second rotary shaftfor rotating one of said curved crystals onto said diffracting positionin accordance with the rotation of said slit means.
 2. An X-rayspectrometer as claimed in claim 1, wherein said first rotary shaft iscoupled with a second rotary shaft penetrating a wall of said vacuumchamber, and a portion of said first rotary shaft protruding from saidvacuum chamber is provided with a rotation driving means.
 3. An X-rayspectrometer as claimed in claim 1, wherein said second rotating meansincludes said second rotary shaft and a rotor fixed thereto, said rotorhaving on the surface thereof said curved crystals arranged in such amanner that said curved crystals are disposed on the same circle havingas the center thereof said second rotary shaft.
 4. An X-ray spectrometeras claimed in claim 1, wherein said second rotary shaft penetrates awall of said vacuum chamber, and a portion of said second rotary shaftprotruding from said vacuum chamber is provided with a second rotationdriving means for rotating said rotor.
 5. An X-ray spectrometer asclaimed in claim 1, wherein said first rotating means is rotated by afirst rotation driving means, and said spectrometer further comprises aninterlocking means for rotating said second rotary shaft in accordancewith the rotation of said first rotating means.
 6. An X-ray spectrometeras claimed in claim 1, wherein said second rotating means is rotated bya second rotation driving means, and said spectrometer further comprisesan interlocking means for rotating said first rotary shaft in accordancewith the rotation of said second rotating means.